Silk screen apparatus for printed circuit boards



United States Patent [72] Inventor Frank Wahl North Bergen, NewJersey [21] AppLNo. 722,598 [22] Filed Apr1119,1968 [45] Patented Dec. 1, 1970 [73] Assignee Western Electric Company, incorporated New York, New York a corporation of New York [54] SILK SCREEN APPARATUS FOR PRINTED CIRCUIT BOARDS 8 Claims, 10 Drawing Figs. [52] U.S.C1 1111/35, 101/123, l0l/l26; 214/1: 198/27, 198/24, 198/218, 198/41 294/655; 74/30, 74/33; 269/8 [51] Int. Cl. B4lll7/36 [50] FleldolSeareh 101/35, 123, 124, 126; 214110112, 10314, 1(B)52. 1(B)54; 198/27, 24, 218; 269/8; 294/655; 74/30, 33 [56] References Cited UNITED STATES PATENTS 1,368,780 2/1921 Anderson 198/27UX 1,547,146 7/1925 Peiler 198/27UX 2,694,973 11/1954 Shoemaker.... 101/126 2,783,709 3/1957 Thomas 101/123 2,793,586 5/1957 Arelt 101/123 2,802,586 8/1957 Wingard.. 198/27X 2,863,382 12/1958 Giani 101/123 2,894,616 7/1959 Young 198/218 Primary Examiner-Robert E. Pulfrey Amlrtant Examiner-Clifford D. Crowder Attorney-H. J. Winegar, R. P. Miller and A. J. Nugent ABSTRACT: Apparatus for silk screening circuit boards including a pivotal loader which transfers a circuit board to an index table. Magnets on the loader and the table hold the circuit board in aligned position for a printing operation. The table indexes the board to a silk screen printing station. The screen is supported over the nested circuit board. A motor driven cam wheel is subject to a single revolution of turning for each cycle of the circuit board printing operation, and drives a carriage back and forth across the screen. The carriage supports a print squeegee and flood squeegee. The print squeegee is lowered to ink the screen and print the circuit during the forward half cycle of operation while the flood squeegee is lowered to spread the ink on the screen during the return half of the cycle of operation. The board is then indexed to an ejection station where it is removed from the indexing table.

Patented Dec. 1, 197 0- Sheet Patented Dec. 1, 1976 Sheet Patented Dec. 1, 1970 Sheet Patented Dec. 1, 19!) Sheet 5 1's SILK SCREEN APPARATUS FOR PRINTED CIRCUIT BOARDS BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to apparatus for silk screening printed circuit boards, and in particular, to apparatus for printing an adhesive ink circuit on an epoxy-coated metal substrate wherein the circuit board is held by magnets on an index table which moves the boards individually to a printing station. A carriage driven by motor means undergoes travel in opposite directions across the silk screen, and in correlation therewith, print and flood squeegees carried by the carriage alternately engage the silk screen. The print squeegee wipes the screen for inking the circuit board during the forward stroke of the carriage, and the flood squeegee loads the silk screen with ink during its return stroke to accumulate ink for the next print stroke. The invention is particularly suited to satisfy the demands for the mass production of printed circuits with preci sion and a high degree of accuracy.

2. Description of the Prior Art Silk screen circuit boards are printed by hand, semiautomatic and fully automatic apparatus. Uniform quality and precision silk screen printing is difficult to achieve if large runs of circuit boards are to be printed quickly and accurately on a mass production basis. In comparison, the hand operation is relatively slow and inefiicient. consequently, many systems and apparatus, semiautomatic and automatic, have been devised to provide precision and uniform quality mass production silk screen printing of circuit boards. These systems and equipments although successful in applying the printed circuit to the circuit board are relatively complex in structure and mode of operation. The problems normally involve the need for loading and alining the circuit boards in the apparatus for printing operation. The mechanical and electrical drive means for operating the apparatus are also a source of much design and operational difficulties. As a result, the known prior art systems are encumbered by extremely complex apparatus which require close attention and maintenance during operation to avoid spoilage and for controlling the application of a uniform circuit pattern by print Squeegees.

SUMMARY OF THE INVENTION The instant invention is directed to applying an adhesive ink to an epoxy-coated metal substrate and includes permanent magnets for loading and holding the circuit boards on an indexing table. The boards are accurately alined for the printing operation when mounted on a loader whereby such alinement is maintained upon transfer to the index table. The index table advances the board to a printing station where the board comes to rest underneath a silk screen supported by suitably positioned silk screen table. The latter supports a relatively simple mechanical system in the form of an oscillating squeegee carriage driven through a forward stroke and return stroke across the screen for each cycle of printing operation. During the forward stroke, the printing squeegee engages the screen for effecting the application of ink to the circuit board. At the conclusion of the stroke, the print squeegee is raised from the screen and a flood squeegee engages same for the return stroke of the cycle of operation, whereby ink is accumulated for the next print operation.

The foregoing mechanism is driven by a cam wheel powered by a motor, and a link rod connecting the wheel to the carriage which imparts oscillating motion to the carriage and the squeegee operating mechanism within the carriage. The squeegee operating mechanism in the carriage includes a pair of juxtaposed oscillating racks both driven by a pinion journaled therebetween under an arrangement whereby the squeegees alternately engage the screen during a full cycle of carriage movement, and alternate their respective positions at the end of each print and flood stroke.

The loader is a flat plate with alinement devices. and when flapped over the table, nests the circuit board on holding magnets and end rests. The ejection mechanism encompasses an air cylinder for lifting a printed circuit board from its nest and pushing such board off the table without damage to its printed circuit. The entire apparatus and system is powered by air cylinders and an electrical circuit as illustrated herein which can be easily modified by one skilled in the art to render the apparatus completely automatic.

Accordingly, it is the principal object of the invention to provide reliable and efiicient apparatus for silk screening printed circuits on large runs of circuit boards with precision and accuracy while meeting the demands of mass production needs.

It is a further object of the invention to provide a simple loader structure adapted to aline and hold the circuit board by magnetic attraction and transfer the board to a magnetic nest in an indexing table without loss of circuit board alinement for printing the circuit thereon.

It is a further object of the invention to provide a mechanically simple squeegee power drive for alternately applying print and flood squeegees to the silk screen wherein the squeegees operate under suitable pressure and at a proper angle to print and accumulate ink on the screen for effecting the desired printing operation.

It is a further object of the invention to provide a relatively simple and reliable ejector mechanism for pushing the circuit board off the indexing table after printing the circuit thereon.

Further objects and advantages will become apparent from the following description of the invention taken in conjunction with the FIGS. in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a top plan view of screen printing apparatus in accordance with the invention;

FIG. 2 is a front elevational view of the apparatus shown in FIG. 1;

FIG. 3 is an elevational and fragmentary view taken along line 3-3 of FIG. 1 and illustrates the loading apparatus;

FIG. 4 is a section through line 4-4 of FIG. I of the loading apparatus;

FIG. 5 is an elevational view taken along line 5-5 of FIG. 2 and illustrates the squeegee carriage structure and the mechanism for driving same;

FIG. 6 is an elevational view in section of the print squeegee;

FIG. 7 is a side elevational view taken along line 7-7 ofFlG. l and illustrates the unloading mechanism;

FIG. 8 is a fragmentary illustration taken along line 8-8 of FIG. 7;

FIG. 9 is an illustrative electrical circuit which may be used for operating the apparatus shown in the foregoing FIGS. and

FIG. I0 is an elevation showing the trolley friction block.

Reference is now made to the FIGS. for a description of the illustrated embodiment of a screen printing apparatus IS in accordance with the invention. A conventional geneva drive movement is enclosed in a housing I6 (FIG. 2) mounted on a support structure 17 which may be fixed to the floor. The geneva movement is indexed by a plunger rod (not shown) of an air cylinder 18 held by brackets 19 to support 17. An index table 20 is keyed to a shaft 21 to turn clockwise, FIG. I, which shaft is driven by the geneva movement.

The upper side of table 20 contains eight nests 22, each for supporting a circuit board on which an adhesive ink pattern is stenciled by apparatus 15. The circuit board 23 shown in phantom in FIGS. I and 3 is an epoxy-coated metal substrate. Each nest 22 includes a pair of plastic rests 24 and four magnets 25 bolted to table 20. Each nest 22 also has a slidable plunger 60 mounted in a sleeve which is clamped to table 20. When a nest 22 is occupied by a circuit board, plunger 25 strikes and depresses a spring return switch arm 26 to close a microswitch 27 at the silk screen printing station. This action energizes a relay CR2, FIG. 9, line 7, which initiates a cycle of squeegee operation as described hereinafter in greater detail.

workpieces (the circuit boards 23) are manually loaded at station 28. FIG. 1. The loading mechanism includes a pivotal loader 29 of nonmagnetic material bolted at 30 to a shaft 31 journaled at opposite ends by a frame structure 32 supported on an extension 33 of support structure 17. Frame structure 32 includes a housing 34 which has a vertical guideway 35 (FIG. 3) containing a movable rack 36 which engages a pinion 37 mounted on shaft 31 to turn same about its axis. Rack 36 is driven by an air cylinder 38 having two air supplies to raise and lower rack 36. When rack 36 lifts, it turns loader 29 counterclockwise (FIG. 3) to transfer a workpiece onto the nest 22 at the loading station. Rack 36 reaches its upper limit at the same time loader 29 is at its extreme counterclockwise posi tion at which time rack 36 closes a limit microswitch 39.

Switch 39 is in series with a microswitch 40, FIG. 9, line 4. Switch 40 is in the ejection mechanism at the unloading station 41. When the series switches are closed. a relay CR1, FIG. 9, line 4, is energized which energizes a solenoid S1(R) (FIG. 9, line which operates air cylinder 38 to drop rack 36 thus causing loader 29 to pivot clockwise to its open position where it is held by a stop 42. Stop 42 is supported by a bracket 43 bolted to extension 33.

A pair of magnets 44 are secured at 45 to loader 29, FIGS. 3 and 4. The pole faces of magnets 44 lie in the plane of loader surface 61, but are exposed by openings 46. The workpiece 23 is manually mounted on surface 61 over the magnet poles and held thereto by reason of magnetic attraction with the substrate. Proper alinement of the workpiece is assured by four spring loaded pilot pins 47, an L-shaped ledge 48 bolted to the end of loader 29, and a pair of upright pins 49. The side and end edges of the mounted workpiece abuts against ledge 48 and pins 49.

Each pilot pin 47 has an exposed tapered end for engaging a pilot hole in the workpiece. The lower end of pin 47 (FIG. 4) rests upon a depressed spring 50 mounted in the interior of a cylinder 51. Cylinder 51 and its spacer 52 are clamped to the underside of loader 29. The clamp structure also includes a plug 53 mounted in a recess on the loading side of loader 29, and has an end threadedly engaging a bore of cylinder 51 for adjusting the spring bias on pin 47. The shank of pin 47 ex tends through a bore in plug 53. Plug 53 includes a collar 54 engaging a recess shoulder 55 for limiting spring compression.

Loader 29 also includes a slidable pin 56 held by a bracket 57 carried by loader 29. The upper end of pin 56 extends above surface 61 of loader 29 and is thus depressed by a mounted workpiece held by magnets 44. The depressed pin 56 closes a microswitch 58. Pin 56 is returned to its extended position by the spring biased switch button upon removal of the workpiece. A relay CR4 (FIG. 9, line I) is energized when switch 58 closes. This action energizes solenoid S1(F) which initiates operation of air cylinder 38 to flap loader 29 counterclockwise for transferring a workpiece to the adjacent nest 22.

The surface of the workpiece 23 to which the ink is to be applied should face upwardly when mounted on its nest 22. Consequently, the workpiece is mounted with such surface confronting ioader magnets 44. The alined workpiece readily transfers from the flapped loader 29. shown in phantom in FIG. 3, to the underneath nest 22. The transfer is efi'ected by the reason of the magnetic force of the four nest magnets overpowering the holding force of the two loader magnets 44. The transfer is essentially an extremely small vertical and straight displacement of the workpiece without any rotation of same about a vertical axis. Hence, the workpiece alinement is maintained for the screen printing operation.

The nested workpiece rests on the pole faces of magnets 25, whereas the opposite ends of the workpiece are supported by rests 24. The rests 24 and magnets 25 form a horizontal surface for supporting the nested workpiece. The clearance (shown in phantom in FIG. 3) between such horizontal surface and the confronting surface 61 of the flapped loader 29 is occupied by the workpiece.

Energization of relay CR1 (FIG. 9, line 4) also energizes a solenoid 53 (FIG. 9, line 6) which actuates air cylinder 18 to index table 20 whereby each nest is advanced on set. i.e.. 45 for an eight nest table. Assuming that the nest advanced to the printing station 59 is occupied by a workpiece, plunger 60 is held down by abutting the workpiece to strike and depress switch arm 26 to close switch 27. This action energizes relay CR2 (FIG. 9, line 7) which, in turn. energizes a motor 62. and as seen hereinafter motor 62 turns a cam wheel 65 one revolution.

The absence of a workpiece upon a nest at printing station 59 will allow the spring biased switch arm 26 to raise plunger 60, whereby switch 27 does not close. This problem may be bypassed by manually loading the nests preceding the printing station 59. The circuit boards printed under such circumstances may be discarded as waste if the circuits applied thereto are not properly oriented on the circuit boards.

Motor 62 drives a shaft 63 through a gear reducing box 64, see FIGS. 1, 2 and 5. The wheel 65 is mounted eccentrically on shaft 63 and turns clockwise therewith. The turning axis of shaft 63 is off the center of wheel 65. whereby the peripheral surface 66 of wheel 65 provides an eccentric cam effect for reasons described hereinafter. The foregoing structure is supported by a bracket 67 carried by a silk screen table 68. A silk screen 69 is held in a recess of a frame 70, which frame is removably secured to table 68 by bolts 71. Table 68 is pivotally supported at its left end (FIGS. 1 and 2) by alined support pins 72 having tapered bearing ends engaging opposite sides of table 68. The threaded shanks of pins 72 are supported by and clamped to respective walls of a supporting frame 73, which frame, in turn, is carried by the upper slide of dove-tail compound slides 74. 75.

With respect to FIG. 2, upper slide 74 in cooperation with its micrometer feed, regulates table 68 for left-right adjustment. The lower slide 75 with its micrometer feed provides table adjustment into and out of the plane of the drawing whereby table 68 and thus silk screen 69 is adjustable for both dimensions in a plane parallel to and adjacently above the workpiece at print station 59. This arrangement provides micrometer positional alinement of screen 69 in order to lay a printed circuit properly on a run of workpieces. The silk screen 69 actually does not make contact with the workpiece. A small clearance exists therebetween during the print and flood cycle of operation. Table 68 is actually held substantially horizontal by resting on a hollow column 76 clamped to support 17 at the right (FIG. 2) of the pivot axis defined by pins 72. Column 76 has an open upper end. A reinforcing plate 77 secured to table 68 rests on column 76. An air cylinder 78 has a plunger 79 which is normally contained in column 76. Actuation of air cylinder 78 extends its piston rod 79 upwardly out of column 76 and against plate 77 to pivotally raise table 68 a fixed angular distance about the axis of pins 72 to allow access to the equipment of the apparatus 15 normally covered by table 68 for the purpose of maintenance, repair and adjustments thereto.

A print squeegee 80 and a flood squeegee 81. each clamped at 82, are carried by respective racks 83, 84. Racks 83,84 are mounted in a trolley for vertical up and down travel. For the purpose of this application the terms trolley and carriage are synonymous. A pinion 86 is journaled in trolley 85. Pinion 86 is turnable about its axis as it engages and drives the opposed racks 83. 84. Clockwise turning of pinion 86 (FIG. 2) raises the printing rack 83 as the flooding rack 84 lowers. Conversely. counterclockwise turning of pinion 86 raises rack 84 and lowers rack 83. Trolley 85 is mounted on a pair of guide rods 87 for slidable travel therealong. Rods 87 extend across silk screen 69 and are supported by brackets 88 secured to table 68.

Trolley 85 is designed to travel left to right (FIG. 2) and return to its start left end position along guide rods 87 for each revolution of turning of wheel 65. The start position is depicted by the phantom illustration 80A of the print squeegee which is to the left of the silk screen pattern over the nested workpiece at printed station 59. The start of the second half of the cycle of operation is depicted by the phantom illustration 81A of the flood squeegee to the right of the silk screen pattern.

A pendulumlike swingable crank 89 extending out from trolley 85 is connected to pinion 86 to turn the latter about its axis. A linkage rod 90 is connected at one end 91 to wheel 65 by a ball-loop universal joint, and by a similar connection at its other end 92 to crank 89. Pinion 86 and crank 89 may be a single unit with its crank handle extending out from trolley 85 to make the connection 92 with rod 90. Rod 90 is made up of telescoped threaded sections so that it may be adjusted for a proper length.

Stops 93 and 94 at the upper ends of respective racks 83, 84 alternately abut against the top wall of trolley 85. Stop 93 is adjusted to make such abutment when rack 83 lowers in response to the wheel-rod connection 91 sweeping through its 9 oclock dead center position (FIG. 21). When wheel 65 thereafter turns clockwise, connection 91 sweeps through its are from 9 o'clock to the 3 oclock dead center as stop 93 remains fixed against trolley 85. This arrangement causes rod 90 to push crank 89 and pinion 86 counterclockwise until pinion 86 becomes locked in a fixed counterclockwise limit position because of stop 93. The resulting action follows as the wheel-rod connection 91 sweeps through its upper are from its 9 oclock position to its 3 oclock position. Trolley 85 is driven from its left end start position to its right end position along guide rods 87. Rack 83 is locked and held in its lower position whereas rack 84 is held in raised status. Print squeegee 80 engages the screen 69 and prints a circuit on the workpiece at station 59. The raised rack 84 holds the flood squeegee 81 in raised status in order that it avoids the silk screen 69.

As connection 91 sweeps through its 3 oclock position and enters the return are from 3 o'clock through 9 oclock, trolley 85 reaches its extreme end position of the printing stroke to the right of the workpiece. Rod 90 now pulls upon and turns crank 89 and thus pinion 86 clockwise. This action lowers rack 84 until stop 94 locks against trolley 85, whereby pinion 86 and crank 89 are held in their respective clockwise limit positions. The flood squeegee 81 now lowers to about 0.020 of an inch above the silk screen 69 to spread ink over the screen during its return stroke, whereas rack 83 is held in raised status and print squeegee 80 is removed from screen 69. As connection 91 sweeps through the lower arc and arrives at its 9 o'clock position. trolley 85 is pulled by rod 90 across to the left of the workpiece and finally arrives at its start position. During the return sweep, the accumulation of ink at the right end of screen 69 is returned by flood squeegee 81 for the next print stroke. Periodically, the person attending apparatus will supply additional ink to screen 69.

A spring-loaded friction block 132 (FIG. 10) is held by a bracket to trolley 85. Block 132 is made up of two sections 133, 134 held together by a spring-loaded bolt 135 carrying spring 136. The shank of bolt 135 extends through section 133 and is threaded to section 134. The assembled block 132 forms circular bores for sliding along rods 87. Antifriction slots 137 in the block bores prevent binding as the block slides along rods 87. Block 132 holds trolley 85 momentarily on rods 87 against travel therealong when the squeegees are being alternated by reason of vertical travel of respective racks 83, 84. After a squeegee reaches its lowered position, the push or pull by linkage rod 90 on crank 89 overcomes the friction holding force of block 132 and causes trolley 85 to travel along rods 87.

It will be understood that the threaded adjustment of stops 93, 94 define the distances racks 83, 84 are lowered and the are through which pinion 86 and crank 89 swing. Oscillation of rod 90 in cooperation with the alternately locked stops 93, 94 control travel of trolley 85. The described operation is correlated with rotation of wheel 65 through its respective l80 arcs.

A switch actuator 96 is keyed to shaft 63 and turns therewith. Actuator 96 strikes a spring biased switch arm 97 to close a microswitch 98 which stops turning of motor 62 after I complete revolution of wheel 65. A relay CR3 (FIG. 9. line 10) is energized by the closed switch 98 to open contacts CRIS-1 and drop relay CR2 (FIG. 9, line 7). This opens series contacts CR2-3 (FIG. 9, line 9) and stops motor 62. The momentum of motor turning carries actuator 96 slightly past the spring return arm 97. allows switch 98 to return to its normally open status after being momentarily closed by the passing actuator 96 once for each revolution of wheel 65 turning. When motor 62 stops, wheel-rod connection 91 is at its 9 oclock position and actuator 96 is slightly advanced clockwise of arm 97.

An opening 99 (FIGS. 2 and 5) in screen table 68 clears an idler wheel 100 journaled by a support 101 carried by upper slide 74. Wheel 65 is eccentrically mounted on its shaft 63 whereby its peripheral surface 66 engages idler 100 as the print squeegee passes over the end portion of the circuit pattern on screen 69. Thus, when screen table 68 is in the horizontal position (as shown in FIGS. 2 and 5) wheel 65 and idler wheel are not in contact with each other. The pattern is applied to the workpiece when the screen table 68 is in a horizontal position. Further rotation of wheel 65 allows wheel 65 to make contact with idler wheel 100. While wheels 65 and 100 are in contact, screen table 68 is pivoted upward about pivot pin 72. This action causes the right end of table 68 to rise a small distance about pivot pins 72 to provide a clean screen printing break away of the trailing edges of the pattern applied to the workpiece.

FIG. 6 illustrates the print squeegee 80 in section. The squeegee wiper 102 may be made of hard rubber material and is bolted between clamp members 103, 104. The wiper assembly is held at a desired angular position by a bolt 105 engaging a slot 106 in a curved holder 107. The upper end of holder 107 extends into an enlarged slot in the lower end of a cylindrical member 108 housed in an outer sleeve [09. A pin 110 secures holder 107 to member 108. The pin-slot attachment allows holder 107 and the attached wiper assembly to experience pivotal play about the axis of pin 110 as the wiper 102 engages screen 69. Cylindrical member 108 has a pin 111 engaging a slot 112 to provide vertical play under spring bias to the wiper assembly. The squeegee is biased by spring 113 contained in sleeve 109 by a threaded plug 114.

The flood squeegee 81 is essentially the same as print squeegee 80 except that the flood squeegee wiper 102 is held in a vertical plane. lts holder 107' is secured to the wiper clamps, (FIG. 5 shows clamp 103' and has a straight upright section attached to a pin-slot assembly in member 108' and sleeve 109 to provide pivotal play about the axis of pin 110'. Squeegee sleeves 109 and 109' are held by respective clamps 82. The squeegees 80, 81 are set for a desired vertical position and held thereat by the set screws of clamps 82.

The workpiece is ejected from the indexed table at the unloading station 41. The unloading station includes an air cylinder 115 (FIGS. 7 and 8) clamped at 116 to opposite guideways 117, 118, which guideways are held by a bracket 119 attached to extension 33 of support 17. A chute 120 held by bracket 119 is located under the ejection end of guideways 117, 118 to receive the ejected workpiece. A slide 121 is recessed in guideways 117, 118 and attached at its upwardly turned front end at 122 to the cylinder piston rod 123. Piston rod 123, normally retracted in its cylinder 115, drives slide 121 back-and-i'orth along guideways 117, 118. A block 124, bolted at 125, is carried by slide 121 for movement along the guideways in response to movement of piston rod 123. Block 124 has a square shaped opening extending vertically for retaining a similar shaped shank 126 which supports a hook 127. Shank 126 is free to slide up and down in the block opening in response to the cam action of a pin 128 riding along the camming surface 129 of guideway 117 in response to movement of piston rod 123. Pin 128 extends outwardly from the top of shank 126. The forward end of slide 121 has an upwardly turned extension 130 for engaging a spring arm 131 of microswitch 40 supported by bracket 119. Extension 1311 engages switch arm 131 to close switch 40 when the piston rod 123 is extended to its forward position at which time the workpiece will have been pushed into chute 120 by the hook 127 Prior to the extension of piston rod 123, slide 121 and the supported block assembly 124 (shown in phantom, FIG. 7) are in retracted position along the guideway. At such time, cam pin 128 engages the lower part of the inclined guideway surface 129 and hook 127 is behind the nested workpiece in a position to engage the end of same. Ejection operation is as follows: when the S2 solenoid (FIG. 9, line 3) is energized in response to closure of switch 58, cylinder piston 123 is extended. Hook 27 engages the workpiece and lifts its end by reason of the camming action of pin 128 riding along surface 129. The tilted workpiece is released from the nest magnets 25 and is pushed forward. When the piston 123 is fully extended, the workpiece falls into chute 120 and extension 130 engages switch arm 131 to close switch 40. When both series switches 39, 40 (FIG. 9, line 4) are closed, relay CR1 energizes whereby its contacts CRl-l (P16. 9, line 1) open to drop relay CR4. This action deenergizes solenoid S-2 and allows cylinder piston 123 to retract to its initial position.

Reference is now made to FIG. 9 for a sequence of operation of the illustrated electrical circuit which supplies line voltage V. Normally, air cylinder 38 is biased to maintain loader 29 in open status to receive a workpiece. When the workpiece is mounted on loader 29, pin 56 is depressed to close switch 58 which energizes a relay CR4 through normally closed contacts (3121-1 and solenoids S-1(F) and 5-2. The foregoing also closes normally open holding contacts CR4-l. S-l(F) is a double solenoid, the other half is S-1(R) (line 5), and the combination is arranged so that only one solenoid of the pair is, at any time, energized. Normally, cylinder 38 is air biased to maintain loader 29 in open position to receive a workpiece. The energized S-l(F) solenoid biases air cylinder 38 to drive rack 36 up to flap loader 29 to its transfer position, in phantom in FIG. 3. The energized S-Z solenoid, which is single acting spring returned, actuates the unloading operation by biasing air supply to cylinder 115 to push a workpiece offthe nest at the unloading position.

Microswitch 39 (line 4) is closed when rack 39 reaches its upper position at the time a workpiece is transferred to a nest on the indexing table 20. Microswitch 40 is closed when piston rod 123 is in its forward position engaging spring arm 131 upon release of a workpiece at the unloading position. Closure of these series switches 39, 40 energizes relay CR1 through normally closed contacts CR2-4 which closes holding contacts CR1-2 (line 5), opens contacts CRl-l to deactivate the firstmentioned circuit (lines 1 and 2) and energizes solenoids S- l(R) and 5-3. Solenoid S-l(R) biases cylinder 38 to return loader 29 to its open position and thus opens switch 39. Switch 40 opens upon solenoid S-2 becoming deenergized to cause retraction of the ejection mechanism.

Solenoid S-3 (line 6) biases cylinder 18 to cause table 20 to index to advance each nest 22 one position. When a loaded nest arrives under silk screen 69, microswitch 27 is closed to energize relay CR2 through normally closed contacts CR2-l and CR3-1 (line 7). initially, the nests between the silk screen 69 and loader 29 may be manually loaded by workpieces to allow continuous operation as described herein. These work pieces may be discarded as waste if not properly silk screened. The energized relay CR2 closes its holding contact CR2-2 (line 8) and opens its contacts CR2-1 (line 7) and CR2-4 (line 4) which drops relay CR1. The energized relay CR2 also closes its contact CR2-3 (line 9) which energizes motor 62 to turn wheel 65 l revolution and thus drives the squeegee trolley 85 through 1 complete operating cycle, whereby the print squeegee 80 is engaged in a forward stroke and the flood squeegee 81 is engaged during the return stroke.

At the start of the motor operation, trolley 85 is at its extreme lefl position depicted by phantom 80A in FIGS. 1 and 2. The print squeegee 80 is in down position and switch arm 96 is clockwise above button 97 of microswitch 98 and rod connection 91 is at a 9 o'clock position, FIG. 2.

The completion of one revolution of cam wheel 65 turning is signalled by switch arm 96 engaging microswitch button 97 which momentarily closes switch 98 to energize relay CR3 (line 10) through normally closed contact CRl-3. This action closes holding contact CR3-2 and opens contact CR3-1 (line 7) to drop relay CR2. The deenergized relay CR2 opens its contacts, lines 8 and 9, to stop motor turning. In the semiautomatic operation contemplated by the illustrated electrical circuit, the operator does not reload loader 29 until after this stage of operation. A workpiece is now manually loaded by the operator attending the apparatus and the foregoing operation is repeated. When the foregoing operation repeats to the point where a workpiece is transferred to the indexing table 20 and switches 39, 40 close to energize relay CR1, its normally closed contact CR1-3 (line 10) open to drop relay CR3.

It will be understood that the foregoing circuit can be replaced by a more complex circuit including timers for making the complete operation of the illustrated apparatus 15 totally automatic wherein all an operator need do is load workpieces on a loader 29 each time an empty nest appears at the loading station 28. While the invention is described with respect to printing a cathalytic adhesive ink pattern on a circuit board preliminary to an electroless deposition of copper on the ink, it obviously can be used for many other purposes and with different materials, e.g. to lay down a pattern of resist material on a copper laminate board prior to etching.

lclaim:

1. Silk screen printing apparatus comprising:

first means for indexing workpieces from station-to-station along said apparatus;

second means for loading workpieces on said indexing means;

third means for unloading workpieces from said indexing means;

fourth means for supporting a silk screen adjacent a workpiece on said indexing means; drive means; fifth means supporting respective ones of a plurality of squeegees for print and flood strokes when a workpiece is adjacent the silk screen, said fifth means including racks which hold respective squeegees and maintain said squeegees in engagement with said silk screen and removed therefrom and including a gear journaled between a pair of said racks for driving said racks in opposite directions; sixth means for operating said fifth means including a linkage response to said drive means for conditioning at least one print squeegee in printing engagement with said silk screen as the flood squeegee is removed from the screen during the print stroke, and for conditioning at least one flood squeegee in ink spreading engagement with the silk screen as each print squeegee is removed therefrom during the flood stroke, said drive means imparting an oscillating motion to said linkage, and said linkage being connected to said gear for positionally conditioning said gear and racks in correlation with motion of said linkage; and

means for positionally locking said racks and gear and allowing same to reverse their respective positions in response to oscillating motion of said linkage.

2. Apparatus in accordance with claim 1 wherein:

said drive means including: a turnable member connected to said linkage, the connection of said linkage to said tumable member is offset from the turning axis of said member; and

said fifth means further including:

guide means extending across said silk screen;

a trolley movable alternately along said guide means and carrying said racks and gear;

the connection of the linkage to the gear correlates the position and movement of said racks and said trolley, said racks reverse position at ends of trolley movement along said guide means in response to reversal of travel of said oscillating linkage; and

friction means for momentarily holding said trolley against travel to allow for alternate positioning of said racks.

3. ln silk screen print apparatus having means for indexing workpieces from station-to-station along said apparatus,

means for loading workpieces onto said indexing means. means for unloading workpieces from said indexing means and drive means, the combination comprising:

first means for supporting a silk screen adjacent a workpiece on the indexing means;

a plurality of squeegees one of which operatively engages the silk screen during the print stroke when a workpiece is adjacent a silk screen and another of which operatively engages the silk screen to spread ink during a flooding stroke;

second means supporting said squeegee for print and flood strokes;

third means oscillating in response to the drive means and operating said second means for positionally conditioning said print squeegee in printing engagement with the silk screen while the flood squeegee is removed therefrom during the print stroke and for positionaily conditioning said flood squeegee in wiping engagement with the silk screen as the print squeegee is removed therefrom during the flood stroke;

a trolley supported by a guideway for travel across said silk screen;

a plurality of racks carried by said trolley and each supporta trolley supported by a guideway for travel across said silk screen;

a plurality of racks carried by said trolley with each rack supporting one of said squeegees;

gear means carried by said trolley and controlling the position of said racks for causing the supported squeegees to make alternative operative engagement with said silk screen; and

means for positionally locking said racks and gear and allowing same to reverse their respective positions in response to oscillation of said third means, said drive means including a motor and turnable member driven by said motor, and said third means including means linking said turnable member and said trolley for correlating trolley travel across the silk screen, the position of said racks and squeegees supported thereby, and turning of said member. 6. ln apparatus in accordance with claim 5 the combination further including a power circuit having:

a first switch responsive to the indexing means positioning a workpiece adjacent the silk screen for actuating said motor to turn said turnable member; and

a second switch responsive to turning the said turnable member and correlating trolley movement through one operating cycle of a print stroke and a flood stroke and for stopping the motor turning upon completion of one cycle of trolley operation.

7. ln silk screen print apparatus having means for indexing workpieces from station-to-station along said apparatus,

ins one ofsaid squeeges; means for loadin work ieces onto said indexin means means.camed by Said t-mney and controlling the posh means for unloadi ng wor l tpieces from said indexii g means tion of said racks for causing the supported squeegees to and drive means, the combination comprising: make alternative operative engagement with said silk i irst means for supporting a silk screen ad acent a workscreen, the squeegees being otherwise held by said racks 4 piece on the indexing means, in a position removed from said silk screen, l f f h i f n I k d d a p ura ity o squeegees one o w ic operatively engages i or posmzna y 0C 5 rac i f the silk screen during the print stroke when a workpiece owmg same {averse respec we ions m is adjacent a silk screen and another of which operatively response to oscillation of said third means; and engages the silk screen to spread ink during a flooding friction means for momentarily holding said trolley against 0 SHORE e 4 i travel to allow for alternate Positioning i racks second means supporting said squeegee for print and flood 4. ln apparatus as defined by claim 3, said drive means in- Strokes, cludmgti dt M b d b t I third means oscillating in response to the drive means and 3 235?" f 2. er y Sal me operating said second means for positionally conditioning w u said print squeegee in printing engagement with the silk means imkmg mmable trolley for t" screen while the flood squeegee is removed therefrom {elatmg "P "avei across the screen' the during the print stroke and for positionally conditioning of f F and 'f j supported thereby said flood squeegee in wiping engagement with the silk F 0 said mefnberi an screen as the print squeegee is removed therefrom during said linking means being connected to said turnabie the flood stroke.

"E a P Off set {aspect to the a shaft for turnably supporting a pivotal plate, said indexing of said member and also being cmnecled to Said means having spaced apart nests for holding individual 3 f" means workpieces and said loading means including said pivotal l Silk Screen P l pp s having means for indexing plate, said pivotal plate being movable between an exwoi'kpleces m statloniosl-auon aiollg Said PP posed position for receiving a workpiece which includes means for loading workplefies onto "l i means magnetic material and a transfer position juxtaposed and means. for unloading fP F from fi "ldexmg means contiguous a nest on said indexing means for releasing the and drive means, the combination comprising: workpiece 0 such nest;

first. means suplfomng a screen adlacem a work magnetic means carried by said plate for holding a work' piece on the indexing means; piece thereto;

a p i y of q gf one whlch Operamely 98 magnetic means in said nest for forcing a workpiece to the s lk screen du g the P stroke f' WOYKRIBCB travel from said plate to said nest when said plate is in its is ad acent a silk screen and another of which operatively t a f i i 8 8 the screen to spread during a flooding means on said plate for alining a workpiece and wherein the Stroke; set alinement of the transferred workpiece is retained for second means suPPclmng Sald squeegee for P and flood receiving a silk screen pattern by reason of magnetic strokes; transfer to said nest,

third means oscillating in response to the drive means and means f lli g ov nt of aid ivotal late operating said second means for positionally conditioning between its positions and having a gear to turn said shaft said print squeegee in printing engagement with the silk and a translatable rack for driving said gear; and screen while the flood squeegee is removed therefrom power circuit means for actuating travel of said rack to during the print stroke and for positionally conditioning pivot said plate to its transfer position and including a first said flood squeegee in wiping engagement with the silk switch responsive to loading a workpiece on said plate screen as the print squeegee is removed therefrom during and a second switch responsive to arrival of the plate at its the flood stroke; transfer position for causing return travel of said rack.

8. In silk screen print apparatus having means for indexing workpieces from station-to-station along said apparatus. means for loading workpieces onto said indexing means, means for unloading workpieces from said indexing means, and drive means, the combination comprising:

first means for supporting a silk screen adjacent a workpiece on the indexing means, said indexing means having spaced apart nests for holding individual workpieces thereon;

a plurality of squeegees one of which operatively engages the silk screen during a printing stroke when a workpiece is adjacent a silk screen and another of which operatively engages the silk screen to spread ink during the flooding stroke;

second means supporting said squeegees for print and flood strokes;

third means oscillating in response to the drive means and operating said second means for positionally conditioning said print squeegee in printing engagement with the silk screen while the flood squeegee is removed therefrom during the print stroke and for positionally conditioning said flood squeegee in wiping engagement with the silk screen as the print squeegee is removed therefrom during the flood stroke;

a piston rod supported adjacent a nest at the unloading station of said apparatus and having an ejection stroke for unloading workpieces;

means including a hook member initially alined for engaging a workpiece on said last-mentioned nest for lifting and sliding the workpiece therefrom, and cam means cooperating with said hook member for lifting the engaged workpiece from said nest during the ejection stroke of the piston rod, said indexing nests having magnet means for holding the workpiece thereto, the workpiece being released by the nest magnet means upon lifling of the workpiece by said hook member; and

the unloading means further comprising:

a guideway and a slide movable in the guideway and attached to said piston rod to move therewith;

a block carried by said slide and slidably supporting said hook member to raise and lower said hook in response to said cam means; and

said cam means including a pin on said hook member and engaging a camming surface along said guideway. 

